1. Field of the Invention
This invention relates in general to certain new and useful improvements in telephone line monitoring apparatus and, more particularly, to a device which is capable of monitoring a wireless subscriber unit which provides an interface between an analog or digital network and a subscriber""s premises telephone wiring and isolating of the phone loop when the voltage falls below a predetermined level.
2. Brief Description of the Related Art
Wireless subscriber telephone units are now becoming quite prevalent throughout much of the world. These wireless telephone units include wireless transmitter and a receiver capable of communicating through a subscriber network to a base station located at a cell site. In fact, in many third world countries, wireless telephone subscriber units are becoming more prevalent then in the United States. The subscriber unit also provides an interface to the subscriber premises telephone wiring.
In many cases, there are still telephones which are hard wired to a central station for operation in many countries, as in much of the United States. The wireless telephone units by definition do not operate through a hard wire circuit. Although cordless telephones do operate through a hard wired circuit, they are considered to be hard wired telephone systems and not subject matter for use in the present invention. In addition, many subscriber telephone units are operable with cable subscriber units and, here again, the mode of operation is similar to that of an analog or a digital network.
In the event of an interruption in telephone service, the user of the wireless telephone system is frequently unable to locate the source of the problem. That source may be a malfunctioning telephone unit or it may well be a short or an open circuit in the wiring between the telephone unit and the subscriber unit. Further, a short could exist between the monitoring device and the telephone. Abnormal loop conditions within the subscriber""s premises may exist, in effect, between the subscriber unit and the monitor or otherwise between the monitoring unit and the telephone unit. It would be desirable to provide a device which allows for monitoring of a wireless telephone system.
In many cases, the wireless communication to the subscriber""s premises may be digital and in many cases it may be a analog. It would therefore be desirable to provide a device which is capable of operating with both digital and analog units to monitor same and which device could also provide for isolation. While a network operator or repair service may be able to determine if a fault has occurred because of the wireless connection, a monitoring device is nevertheless required to determine if there was a fault within the subscriber""s premises.
The need for monitoring a telephone loop is also becoming important in those cases where gates and other security accesses are connected directly through a telephone system. It is important to insure that a breach of security does not result by purposely cutting a telephone line or otherwise attempting to interfere with a telephone network. Thus, it would be important to enable monitoring of a system, even where a breach in that system has resulted.
Although there are no known prior art teachings of a solution to the aforementioned deficiencies and shortcomings, such as those disclosed herein, U.S. Pat. No. 4,390,750 to Bartelink (Bartelink), U.S. Pat. No. 4,446,340 to Fryer (Fryer), and U.S. Pat. No. 4,417,137 to Rosenfeld, et. al (Rosenfeld) discuss subject matter that bears some relation to matters discussed herein. Bartelink discloses a remote supervisory system for monitoring the status of a subscriber""s premises over existing telephone circuits from the central office. Auxiliary equipment at the subscriber""s premises is coupled to the subscriber""s telephone circuit and includes sensors which monitor the condition of the premises. If an abnormal condition is sensed, the auxiliary equipment notifies the central office which may further notify an action center at that central office of the subscriber""s identity and nature of the alarm.
Fryer discloses a loopback circuit for testing a telephone line between the central office and a subscriber""s equipment. The loopback circuit is located at the subscriber""s end of the line and is powered by the normal central office power source. Fryer injects a signal from the central office to actively test the telephone line. Thus, Fryer does not provide a stand alone capability, or a passive capability to monitor the subscriber""s premises and report alarm conditions without a wire line connection to the central office.
Rosenfeld discloses an apparatus for monitoring the hook status of a remote telephone. Rosenfeld introduces a disturbance voltage signal onto the subscriber loop from the central office, and then monitors variations in impedance in the subscriber loop. Thus, Rosenfeld does not provide a stand alone capability, or a passive capability to monitor the subscriber""s premises and report alarm conditions without a wire line connection to the central office.
With any existing wireless telephone system, there is presently on-premise monitoring with a wireless telephone system and an alarm circuit arrangement used in combination therewith. However, where an alarm would occur with an existing alarm apparatus, it is necessary to isolate the telephone wiring of the premises from the alarm circuit, particularly as connected through tip ring conductors, so that the alarm has a priority of use in the communication path to the telephone network. If this is not achieved, an initiation of an alarm signal to a central station or other monitoring facility, such as a police department, will not be enabled. Thus, there is a need as well for a system which will provide the capability of communicating an alarm status, even during an existing telephone call in the premises.
It is, therefore, one of the primary objects of the present invention to provide a subscriber premises telephone loop monitoring and isolation device which can be installed both internal to or as an adjunct to a wireless subscriber telephone unit.
It is another object of the present invention to provide a subscriber premises telephone loop monitoring and isolation device which is capable of providing an interface between both an analog telephone wireless network and a subscriber premises telephone wiring system.
It is a further object of the present invention to provide a subscriber premises telephone loop monitoring and isolation device of the type stated which is also effective in operating with a cable or wireless subscriber unit and providing a similar mode of operation therefor.
It is an additional object of the present invention to provide a telephone loop monitoring and isolation device of the type stated which provides passive and real time loop status information to a subscriber unit, as well as loop isolation if the voltage across the loop falls below a predetermined value.
It is another object of the present invention to provide a monitoring and isolation device for use on the subscriber""s premises, of the type stated, which will automatically provide a loop-cut through between the telephone unit and the subscriber unit even if a power failure occurs during an active telephone communication.
It is also an object of the present invention to provide a telephone loop monitoring and isolation device of the type stated which is capable of automatically restoring normal telephone loop operation when the impedance conditions are restored to a proper level and the subscriber""s premises loop is automatically reconnected to the subscriber unit.
It is still another object of the present invention to provide a telephone,loop monitoring and isolation device of the type stated in which loop status information can be provided directly to a subscriber via the telephone loop monitoring and isolation device.
It is another salient object of the present invention to provide a method of monitoring a wireless subscriber telephone unit between an analog or a digital wireless network and isolating same when voltage across the loop drops below a predetermined value and to automatically restore operation when loop impedance conditions have been restored.
It is still a further object of the present invention to provide a system which enables alarm status indication through a subscriber unit in a wireless network operation so that a signal path can be maintained simultaneously to a voice or data telephone call while still providing an alarm signal.
With the above and other objects in view, our invention resides in the novel features of form, construction, arrangement and combination of parts and components presently described and pointed out in the claims.
A telephone loop monitoring and isolation device which may be in the form of a small box-like unit having a size substantially less than a hand-held subscriber telephone unit. The device of the present invention may be arranged to be internal with or otherwise used as an adjunct to a wireless subscriber unit. The device of the invention which provides both monitoring and isolation will thereby provide an interface between both an analog or a digital wireless network and a subscriber""s premises telephone wiring system.
The device of the invention is also operable with a cable subscriber unit in which the modes of operation are similar to those of a wireless subscriber telephone unit. The monitoring device is effective in that it will provide both passive real time loop status information through an interface to the subscribers telephone unit. The device of the invention will also provide loop isolation if the voltage across the loop falls below a predetermined voltage level as, for example, a 5 volt DC level. In like manner, it will also provide isolation if the loop is short-circuited, such as if the voltage falls to zero or a low voltage such as one volt.
When normal loop impedance conditions are restored, such that the voltage may be elevated back to a voltage above five volts, and the impedance is established to the predetermined value, the subscriber""s premises telephone loop is automatically reconnected to the subscriber unit. In this way, normal telephone operation is restored and the updated loop status is communicated to the subscriber unit by the telephone loop monitoring and isolation device of the invention.
If the telephone loop monitoring and isolation device is not internal to the subscriber telephone unit, that is, not integral with the subscriber unit as a single unit, the status of the loop interconnecting the telephone loop and the monitoring and isolation device is also checked for open circuit conditions or otherwise abnormal impedance conditions. In addition, the device of the invention will automatically provide status information to the subscriber preferably, although not limited to, visual loop status information. In addition, operation in a xe2x80x9cstand alonexe2x80x9d mode of operation can be obtained by connecting the telephone loop monitoring and isolation device directly to an analog telephone network. It should be recognized that any connection to a cable or wireless network must be through a subscriber unit, thereby providing both monitoring of the loop and of the subscriber""s premises wiring. The status information is also available in this latter mode of operation by interfacing to a home/office monitoring system, if desired.
The monitoring and isolation device of the present invention is operable in numerous circuit configurations as, for example, with a wireless subscriber telephone unit and with the monitoring and isolation device functioning either external to or otherwise internal to the wireless subscriber telephone unit. The device can also be operated with a cable subscriber unit, as previously described. In addition, the telephone monitoring and isolation device of the invention is operable with no subscriber unit, such that telephone service to the subscriber""s premises is provided by a copper loop interface through a public switched telephone network.
When it is desired to isolate a specific loop within a premise and an associated telephone system connected to the loop, an additional telephone loop monitoring and isolation device of the invention can be used. The placement of the device in this case also is exemplary of the situation in which a fax and a telephone are both connected to a common telephone loop. In this case, the status of the loop can be monitored and fault isolation can also be obtained supplementary to the monitoring device integration with the unit. Further, the telephone loop monitoring and isolation device of the invention could be integrated into a power surge suppressor for providing both surge protection and loop status monitoring information and fault isolation.
The circuit arrangement forming part of the monitoring and isolation device of the present invention is specifically divided into several circuits and include, for example, a sensing circuit which senses initial voltages on the subscriber line and particularly on the link between the central telephone switching station and the subscriber unit, the tip-ring paired conductors from the subscriber unit to the monitoring and isolation unit of the invention and the tip ring pair of conductors from the monitoring and isolation device to the telephone.
A comparator circuit receives the input voltages and compares these input voltages against reference voltage levels so as to determine if there is a short or an open circuit condition on any of the lines previously described. Connected to the output of the comparator circuit is an indicator circuit. This indicator circuit provides transistor logic level inputs which can be connected directly to the subscriber unit for alerting the subscriber unit to potential deleterious conditions. The indicator circuit also provides voltages for light emitting diodes or other indicators, such as sound indicators or the like, to alert a user of a short or open circuit condition or, otherwise, even a normal circuit condition.
The present invention further includes an isolation circuit which will provide circuit isolation along with a relay circuit. The isolation circuit and the relay circuit operate in conjunction with one another in order to isolate the unit in the event there is a short or open circuit condition in the telephone loop.
In accordance with the present invention, there is also an alarm status interface with the telephone loop monitoring and isolation device of the invention. In the situation where the subscriber unit is in conjunction with a wireless telephone system or cable interface, when replacing the traditional tip-ring connection to the subscriber""s premises, an alarm output would formerly have to be re-routed to the subscriber unit. Thus, if an alarm would occur with an existing alarm monitor apparatus, it would be necessary to isolate the telephone premises wiring from the alarm tip-ring circuit so that the alarm would have priority use in a communication path. If this prioritization is not achieved, then a call from an existing subscriber premises will not be enabled, and will effectively xe2x80x9cbusyxe2x80x9d out the wireless or wire line loop to the central office. This would, in turn, block an alarm call to a monitoring center.
In accordance with the present invention, there is provided an alarm status indication through the subscriber unit back to the monitoring service center or otherwise back to a wireless network operator. With this enhanced signaling path, there can be maintained a simultaneous voice and data telephone call along with an alarm status signal. A signaling path from the subscriber unit delivers an alarm status through a TTL path to the subscriber unit. This TTL path will communicate the alarm status even during an existing and active telephone call at the premises. The invention will also provide subscriber loop isolation so that the alarm unit will have priority of a connection over the tip-ring terminal of the subscriber unit.
This invention possesses many other advantages and has other purposes which may be made more clearly apparent from a consideration of the forms in which it may be embodied. These forms are shown in the drawings forming a part of and accompanying the present specification. They will now be described in detail for purposes of illustrating the general principles of the invention. However, it is to be understood that the following detailed description and the accompanying drawings are not to be taken in a limiting sense.